January 9, 2014

Vultures Wait For Prey Where They’re Likeliest To Die

Vultures are even more conniving than previously believed, searching for food sources in places they know animals are more prone to die. African vultures are seen as the grim reapers of the sky, magically showing up right at the moment when an animal becomes a carcass. The latest study sought to find out how these creatures were able to cover such vast regions to find food in the first place.

Researchers reported in the journal PLOS ONE that rather than hunting in areas where animals are abundant, vultures actually pick out prey by focusing on areas and conditions where animals are most likely to die.

Scientists had previously assumed that vultures simply followed the largest food sources, waiting for one of the animals to drop dead. However, the latest evidence indicates that these birds are considerably more sophisticated.

The team attached GSM-GPS telemetry devices to three species of vultures in Mara-Serengetic ecosystem in East Africa. These devices sent out text messages back to the researchers, giving the team details about the bird’s location and altitude. Data showed that vultures focused on the immense wildebeest herds only during the dry season when hundreds of wildebeest die each day from starvation. The results revealed how vultures preferentially selected areas of low rainfall, where they would find higher prey mortality.

"Our study shows that vultures seek out areas not where wildlife are most abundant, but where they are most likely to die," lead author Corinne Kendall said in a statement. "This shows that for vultures, prey mortality is more important than prey abundance."

From November to June, vultures travel all over Kenya and Northern Tanzania, with some individuals using an area of more than 77,000 square miles, in search of food. However, the birds know where to be during the wildebeest migration period.

"We knew that vultures use efficient soaring flight, keen eyesight, and even used information from each other to find food, but we had a poor sense of how they decide where to search on a landscape scale,” said Keith Bildstein, Director of Conservation Science at Hawk Mountain Sanctuary and a study co-author.

White-backed vultures and Ruppell's vultures, both included in the study, have been listed as “Endangered” by the International Union for Conservation of Nature due to declines seen throughout Africa. Understanding more about how these animals hunt for food could help researchers find out why these vultures are dying off.

"Because the vultures spend so much time outside of protected areas, they are extremely susceptible to poisoning, which often occurs when ranchers put pesticides on the carcasses of cows and other animals killed by lions or hyenas. You can imagine how difficult it is to protect a species that uses not just multiple parks, but also spends a lot of time in areas that are completely unprotected,” explained Munir Virani, Director of Africa programs for the Peregrine Fund and co-author of the study.

Wildlife organizations are now working hard to protect these scavenger birds, which play a valuable role in reducing the prevalence of rabies and other diseases. Dr. Steve Zack, Coordinator of Bird Conservation at Wildlife Conservation Society, said studies like this are important for continuing their efforts.

"This information is critical to understanding the scale of effort needed to protect vulture species in East Africa. The new knowledge makes clear that engaging local communities well beyond park boundaries is needed to confront and eliminate the poisoning,” Zack said.